Research Of Coded Caching Scheme Based On Placement Delivery Array And D2D Placement Delivery Array

With the rapid development of wireless communication network technology,more and more users use multimedia applications such as video on demand,which brings great pressure to wireless communication network transmission.Generally speaking,network transmission can be divided into peak time and off-peak time according to the time-varying of network traffic.During the peak time of network transmission,there are many active users on the network,and the network traffic shows explosive growth,which leads to the network transmission becoming very congested.During the off-peak time of network transmission,there are fewer active users,which leads to the low utilization rate of network resources.In order to solve these problems effectively,researchers put forward coded caching technology.During the off-peak time of network transmission,users can put some popular network resources into their local buffer memory in advance,so that the traffic can be transferred from the peak time to the off-peak time.During the peak time of network transmission,the server only needs to broadcast the encoded data packets to meet the needs of users according to the contents cached by users and the contents requested by users.Therefore,the coded caching technology can greatly improve the transmission efficiency of the network,reduce the network congestion during the peak time,and realize the balanced allocation of network resources.Coded caching technology is widely used in shared-link and Device to Device(D2D)network.Yan et al.and Wang et al.put forward the combined structure of Placement Delivery Array(PDA)and Device to Device Placement Delivery Array(DPDA),thus transforming the problem of constructing coded caching scheme in shared-link and D2D network into the problem of constructing PDA and DPDA.In the current research,the results of PDA and DPDA are few,and the coded caching scheme obtained by PDA and DPDA has two problems.On the one hand,the transmission load or the subpacketization is large;On the other hand,the parameters of the scheme are special.Therefore,it is of great application value and theoretical significance to construct PDA and DPDA with good performance and arbitrary parameters.In this thesis,more kinds of PDA and DPDA are constructed by combination design,and the specific results are as follows:Firstly,using combinatorial design and cyclic orbit method,this thesis constructs a Base Placement Delivery Array(BPDA).Then,a new kind of PDA is obtained by using cartesian product,and the coded caching scheme under the shared-link model is obtained,that is CCW1 scheme.Through theoretical analysis and numerical analysis,under the condition of fixed number of users and user cache ratio,the transmission load of CCW1 scheme obtained in this thesis is the same order of magnitude as that of MN scheme,but the subpacketization in MN scheme is at least2~m that of CCW1 scheme,where m is an arbitrary positive integer;Compared with the WCLC scheme,when the user cache ratio is between 1/3 and 1/2,the transmission load of the WCLC scheme is twice that of the CCW1 scheme,while the subpacketization in the CCW1 scheme and the WCLC scheme is the same order of magnitude;Compared with other coding cache schemes,CCW1 scheme also has certain advantages in the transmission load or the subpacketization.Secondly,using combinatorial design and cyclic orbit method,this thesis constructs a D2D Placement Delivery Array,and then obtains a new coded caching scheme in D2D network environment,that is CCW2 scheme.Through theoretical analysis and numerical analysis,the CCW2 scheme obtained in this thesis is compared with JCM scheme under the condition of fixed user number and user cache ratio.When the number of users approaches infinity,the ratio of the subpacketization between JCM scheme and CCW2 scheme also approaches infinity.Especially when the user cache ratio is close to 1/2,the ratio reaches the maximum;The transmission load of CCW2 scheme is higher than that of JCM scheme,but it is in the same order of magnitude;Compared with some other coding caching schemes,CCW2 scheme also has certain advantages in transmission load or the subpacketization.